Electrode for gaseous discharge lamps



Jan. 17, 1956 H. E. KREFFT ELECTRODE FOR GASEOUS DISCHARGE LAMPS FiledDec. 18 1950 INVENTOR. f/ mm Foz/A/w/(REFF M MUM z ATTORNEY UnitedStates Patent ELECTRODE FOR GASEOUS DISCHARGE LAMPS Hermann EduardKreift, Buenos Aire's, Argentina Application December 18, 1950, SerialN201,331

4 Claims. (Cl. 313-343) The present invention relates to electrodes forelectrical gas discharge lamps and more particularly to activatedelectrodes for high pressureand super high pressure lamps.

The terms high pressure lamp and super high pressure lamp in accordancewith the present invention refer to electrical discharge lamps whichoperateunder pressures of from about one atmosphere and above about tenatmospheres respectively, and which contain, under operating conditions,a metal vapor, e. g. mercury vapor, to which is added an inert gas, orwhich may contain a mixture of metal vapors or a mixture of metal vaporsand rare gases, e. g. krypton and xenon.

In such lamps, as it is known, the discharge forms an arc of hightemperature which, owing to the high current density, is limited to avery small area of the electrode. Consequently, the electrodes areexposed locally to very high temperatures which cause evaporation ofelectrode material. Through this process, electrode life is limited, andthe bulb of the lamp is blackened. Electrodes for high pressure or superhigh pressure lamps are, therefore, mostly made of tungsten, and theyare provided with a certain amount of activating materials through whichtheir temperature is lowered. These activating materials are alsorequired in order to improve starting of the discharge. Such activatingmaterials are the metals barium, calcium, strontium, thorium, or theoxides thereof and the dioxides of thorium and zirconium. However, theseactivating materials, although they lower the temperature of theelectrodes, may produce considerable blackening of the bulb as theyevaporate rather easily. It is, therefore, very important to limit theirquantity, and to add them to the electrode in such a way that theyproduce sufiicient activation without being excessively exposed to theaction of the discharge are.

It is, therefore, one object of my invention to provide an activatedelectrode for high pressure and super high pressure lamps which does notblacken' the wall' of the discharge vessel; another object is to providean electrode which starts easily and without sputtering; still anotherobject is an electrode of the coiled coil type; a further object is anovel electrode of the storage type; another object is an electrode ofthe self heating type. Other objects and advantages of this inventionwill become apparent from the description hereinafter following and thedrawings forming part hereof in which:

Figure 1 is a transverse, partly sectional view of a coil, provided witha core, according to the invention;

Figure 2 is a longitudinal sectional view of a coil, taken on the line22 of Figure 1 illustrating the structure of the core;

Figure 3 is another transverse, partly sectional view of a coilaccording to Figure 1, illustrating the positions of a gas absorbingwire and of the activating material;

Figure 4 illustrates a modification of the arrangement of the corewires;

Figure 5 is a diagrammatic, partly sectional view of a coiled coilelectrode according to the present invention;

2,731,581 Patented Jan. 17, 1956 Figure 6 is another schematicrepresentation of a coiled coil electrode according to the presentinvention.

According to the present invention an activated solid incandescentelectrode of the storage type is formed by a tungsten wirecoilcontaining, in its interior, a core composed of a plurality ofmetallic wires which are preferably twisted, and thus form a rigidsupporting structure for the coil which, inthe spaces existing betweenthe core wires, and between the core and the coil, also contains theactivating materials. This coil is preferably coiled by which means anelectrode of the coiled coil type is produced which possesses amechanically strong structure, and which is provided, in a particularlyconvenient way, with a storage of activating materials. Owing to thisstructure, this novelelectrode isadvantageously used in high pressure,and super high pressure lamps which are started without pre-heating ofthe electrodes, but it can be used also in other .gaseous dischargelamps which are started with cold electrodes.

As shown in Figure 1,- which is a transverse partly sectional view of acoil, the core contained in its interior consists of four metallic wires1', 2, 3, and 4,: on which the coil 5 is firmly connected. The interiorof the coil is not entirely occupied by the core wires which form, withthe coil, and between themselves, channels 6, and 7. In Figure 2' whichis a longitudinal sectional view of the same coil, takenon the line 2-2of Figure l, the core wires 2, and 4-, and the central channel 7, andtransverse sections of the coil 5-, are shown.

Preferably, the coil 5 consists of a tungsten wire, while the core iscomposed of tungsten, molybdenum, tantalum, or thorium,- or of acombination of wires consisting of these metals. A preferred combinationof the core consists of three tungsten wires and one tantalum or thoriumwire. The invention, however, is not limited to the use of four corewires which quantity is indicated by way of example only. As shown inFigure 3, a centrally located fifth core wire 9 may be added to thestructure already described. This central wire may be made either oftantalum or thorium, while the others, 1, 2, 3,. and 4, are tungstenwires, or at leastpartly consist of tungsten, and partly of the othermetals mentioned. The spaces which are formed between the core wires andthe coil, are filled with activating materials 8 composed, for example,of

. the oxides of barium, calcium, strontium, or thorium, or

of zirconium-dioxide, or of mixtures of these materials the particlesize of which should be chosen as small as possible.

This electrode structure olfers many advantages as it combines severalproperties required by high pressure lamps, or other lamps which startwith cold electrodes. In the first place,the coilprovided with a core isan element with considerable mechanical strength which can be utilizedfor the construction of other electrode structures; furthermore, thepockets or channels which exist in the interior of the coil, areexcellent places for the activating materials which must be protectedfrom the direct action of the discharge arc, but should be welldistributed all over the electrode, and close to its surface; anotheradvantage is the use of gas absorbing or activating metals as acomponent of the core. These advantages would not exist if a solid corewere used instead of a plurality of core wires which form a flexiblecore.

Since a core, composed according to the present invention, is flexible,the coil, or primary coil, which I have described may be coiled up toform a secondary coil. To this end, however, it is convenient to twistthe core wires, as shown in Figure 4 which illustrates a coil assemblycomposed of four twisted core wires 1, 2, 3, and 4, and a coil 5.According to Figure 5, an electrode embodying my invention consists of asecondary coil 10 which forms a hollow cylindrical body, supported by acoaxial wire or rod 11 which fits accurately into the interior of thecoil 10. This secondary coil is composed oxides of barium, calcium,strontium, or thorium, or of zirconium dioxide, or of mixtures of thesematerials. The wire or rod 11 consists of tungsten, tantalum ormolybdenum, and it may form simultaneously the inner lead of the leadwire contained in the seals of'the lamp. However, this electrodesupporting wire 11 must not consist of a single wire or rod, as shown inFigure 5, but it may be also composed of a plurality of wires forming asecondary core which has the same structure as the primary corepreviously described. According to another embodiment of my invention,illustrated by Figure 6, the coiled coil electrode structure is selfsupporting, and does not contain a coaxial supporting wire or secondarycore. The electrode shown in Figure 6, is composed of a secondary coilwhich is formed by a primary coil assembly consisting of twisted primarycore wires 1, 2, 3, and 4, a fifth axial core Wire 9, and a primarytungsten coil 5. As already described, the free spaces existing betweenthe core wires, and between these wires and the coil 5, are filled outwith activating materials.

The degree of activation of an electrode according to the presentinvention naturally depends on the choice and proportion of theactivating materials already mentioned, and on the spaces existingbetween the turns of the primary coil. Therefore, the pitch which isgiven this coil during manufacture, which pitch depends on the natureand composition of the activating materials, is an important means ofcontrol of electrode performance. Electrode life also depends on thequantity of activating materials contained in the electrode which isdetermined by the volume of the channels existing in the interior of theprimary coil assembly. Obviously, a desired volume is obtained byproperly choosing size and number of the primary core wires, and thetotal length of the primary coil assembly.

As it is known, electrode performance and lamp life, particularly insuper high pressure lamps, are considerably improved by the use of gasabsorbing materials like tantalum, zirconium, and thorium. According tothe present invention, these materials form part of the primary orsecondarycore of the electrode where they are exposed, under operatingconditions, to temperatures which lie within a convenient range foroptimum gas absorption.

During manufacture of the electrode, the primary coil is produced in acontinuous process which is carried out by a customary coiling machineutilizing the primary core, which is composed of a plurality of corewires, as mandrel wire. After annealing, the second coil is produced onsteel mandrel pins, or on the wire or rod which is used as secondarycore, and given another heat treatment at high annealing temperatures,by which means it obtains a definite shape. Finally, the activatingmaterials are introduced into the interior of the primary coil, which isdone in the usual Way by dipping the electrode into a suspension ofthese materials prepared with a suitable solvent and binder, likeamyl-acetate and nitrocellulose.

What I claim is:

1. An activated electrode for high pressure and super high pressuregaseous electric discharge'devices comprising a core composed of aplurality of refractory metal wires, which are twisted with respect tothe axis of said core, a tungsten wire coil helically wound about saidcore and in contact therewith throughout its length, the pitch of thecoil being very low and constant throughout the length thereof, and theindividual convolutions of said coil being closely adjacent one anotherwhereby said coil forms a protecting wall about'said core and wherebysmall pockets are formed between the coil and the core wires and amongthe core wires themselves throughout the length thereof, saidelectrodebeing in the form ofa coiled coil, an activating material selected fromthe group consisting of barium, calcium, strontium, thorium, andzirconium, deposited in said pockets to form a continuous tortuous pathof activated material and wherein said coil serves to shield, said corewires and activating materials against rapid deterioration by the highpressure discharge.

2. The electrode of claim 1, wherein said core is comprised of aplurality of tungsten wires.

3. The electrode of claim 1, wherein said core is com- 7 prised of aplurality of tungsten wires and at least one wire selected from thegroup consisting of thorium and tantalum.

4. The electrode of claim 1, including a supporting metal wire elementlocated within said coiled coil and about which said coiled coil iswound, said supporting element being taken from the group consisting oftungsten,

tantalum, and molybdenum.

I References Cited in the file of vthis patent UNITED STATES PATENTS

